Apparatus and a method for forming an alloy layer over a substrate

ABSTRACT

One embodiment of the invention involves introducing at least two metals into a chamber for forming an alloy layer over a substrate. This is accomplished by a variety of methods. In one embodiment, at least two metals are mixed and introduced into a chamber in which a focused ion beam contacts the two metals to form at least one alloy layer over a substrate. In another embodiment, at least two precursor gas sources are introduced into the chamber in which each precursor gas source contains a metal. The focused ion beam contacts the two precursor gases to form an alloy layer over the substrate. In yet another embodiment, a second metal layer is formed over a first metal layer to form a multi-metal layer. Thereafter, thermal treatment or introducing a focused ion beam to at least a portion of the multi-metal layer is performed to create at least one alloy layer over the substrate.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to introducing at least two metals into achamber and forming a layer over a substrate, and more specifically, toforming an alloy layer over a substrate.

[0003] 2. Background

[0004] Integrated circuit structures are generally formed of numerousdiscrete devices on a semiconductor chip such as a silicon semiconductorchip. The individual devices are interconnected in appropriate patternsto one another and to external devices through the use ofinterconnection lines or interconnects to form an integrated device.Typically, many integrated circuit devices are formed on a singlestructure, such as a wafer substrate and, once formed, are separatedinto individual chips or dies for use in various environments.

[0005] There are several conventional processes for introducing metalssuch as aluminum, aluminum alloy, or platinum to form an interconnectover a substrate. The metal is generally introduced in the form of adeposition process, (e.g., chemical vapor deposition (CVD), focused ionbeam (FIB) deposition) and patterned by way of an etching process into adiscrete line or lines. FIB deposition is generally used to introducethin metal lines to form a metal pattern or layer over a substrate.Typically, a single metal such as platinum, tungsten, or molybdenum isintroduced over a substrate by a FIB deposition system. Another processfor introducing a metal interconnect, particularly copper or its alloyover a substrate is the damascene process. The damascene processintroduces copper interconnect according to a desired pattern previouslyformed in a dielectric material over a substrate.

[0006] Yet another process is FIB metal deposition which is generallyused to introduce thin metal lines or arbitrary patterns as a layer overa substrate. FIB deposition is used for modification of small metallicstructures such as the modification of existing interconnects inintegrated circuits.

[0007] One disadvantage to these approaches is that the interconnectthat is formed on the substrate has a relatively high electricalresistance such as 160 μohm-centimeters (μohm-cm) to 200 μohm-cm. Thismay be due to the surface property that results from the use of a singlemetal that provides poor bulk electrical resistance or to the existenceof elements like carbon which originate from the precursor. Generally,the resistance of an alloy such as tungsten-carbon-cobalt is lower thanthat of metal alloy such as tungsten-carbon. J. Brooks, Properties ofTungsten Carbide Cobalt Alloy, 232 (1994). What is needed is a processand a tool that allows for the introduction of metals to form a layerover a substrate that decreases the electrical resistance of the layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The features, aspects, and advantages of the invention willbecome more thoroughly apparent from the following detailed description,appended claims, and accompanying drawings in which:

[0009]FIG. 1 illustrates a schematic cross-sectional view of aprocessing chamber suitable for performing the modification described inreference to FIGS. 2-6 in accordance with one embodiment of theinvention;

[0010]FIG. 2 illustrates a schematic cross-sectional view of a portionof a substrate in accordance with one embodiment of the invention;

[0011]FIG. 3 illustrates a schematic cross-sectional view of metalsintroduced over the substrate of FIG. 2 in accordance with oneembodiment of the invention;

[0012]FIG. 4 illustrates a schematic cross-sectional view of metalsintroduced over the substrate of FIG. 3 in accordance with oneembodiment of the invention;

[0013]FIG. 5 illustrates a flow diagram of one method of focused ionbeam deposition of an alloy layer over a substrate in accordance withone embodiment of the invention; and

[0014]FIG. 6 illustrates a flow diagram of one method of forming analloy layer over a substrate by heating a multi-metal layer inaccordance with one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0015] One embodiment of the invention involves introducing at least twometals for forming an alloy layer over a substrate. This is accomplishedby a variety of methods. In one embodiment, at least two metals arepremixed and introduced into a chamber in which a focused ion beamcontacts the two metals to form at least one alloy layer over asubstrate. In another embodiment, at least two precursor gases areintroduced into the chamber in which each precursor gas contains atleast one different metal. The focused ion beam contacts the twoprecursor gases to form an alloy layer over the substrate.

[0016] In yet another embodiment, a second metal layer is formed over afirst metal layer to create a multi-metal layer over a substrate.Thereafter, the multi-metal layer is either thermally treated or afocused ion beam is applied to at least a portion of the multi-metallayer. Thermally treating or applying a focused ion beam to themulti-metal layer results in the metal in the first metal layer reactingwith the metal in the second metal layer. This reaction forms an alloylayer over the substrate. Each of these methods of forming an alloylayer reduces the electrical resistance typically found in a depositedmetal layer of conventional processes.

[0017] The metals selected for this process may include cobalt, metalcarbonyl, molybdenum, tungsten, or a mixture of cobalt, molybdenum,tungsten or any other suitable metal. In the context of the descriptionof the invention, the words cobalt, molybdenum, or tungsten are intendedto refer to both pure cobalt, molybdenum, or tungsten and to theiralloys that are suitable as integrated circuit interconnect material. Inanother aspect, a system is disclosed for introduction of at least twometals into a chamber using the methods described above. In oneembodiment, the system includes a chamber configured to house asubstrate, such as a semiconductor wafer, a discrete chip or a die, andan energy source. A system controller is configured to control theintroduction of metals such as cobalt, metal carbonyl, molybdenum,tungsten, or a mixture of two or more of these metals into an energysource such as a FIB. The system controller also controls theintroduction of the energized metals from the energy source over asubstrate. A memory coupled to the controller includes amachine-readable medium having a machine-readable program embodiedtherein for directing the operation of the system. The machine-readableprogram includes instructions for controlling the amount of metalintroduced into the energy source and controlling the energy source thatintroduces the energized metal into the chamber. In the discussion thatfollows, FIG. 1 illustrates FIB deposition system 103 for FIB depositionand FIGS. 2-6 illustrate the formation of alloy layers over a substrate.

[0018]FIG. 1 illustrates a schematic cross-sectional view of a FIBdeposition system 103 that is used to introduce more than one metal oversubstrate 100 to form an alloy layer over substrate 100. FIB depositionsystem 103 includes chamber 150, first and second reservoirs (183, 185),first and second precursor gas sources (194, 195), third and fourthinlets (193, 196), FIB column 175, heat source 191, and controller 190for FIB deposition of metals such as cobalt, metal carbonyl, molybdenum,tungsten or other suitable metals over substrate 100. Each of thesedevices is described below.

[0019] Chamber 150 is typically constructed of aluminum or steel and hasa suitable inside volume to house a substrate, such as substrate 100. InFIG. 1, substrate 100 is seated on substrate processing stage 160 thatitself is coupled to shaft 165 to support substrate processing stage 160inside chamber 150.

[0020] Coupled to chamber 150 is first reservoir 183 and secondreservoir 185. First reservoir 183 and second reservoir 185 areconfigured to contain a different metal for delivery of the metal ormetals to chamber 150 in, for example, a phase such as a vapor phase.Techniques for placing metals into a vapor phase are known in the artand details of this process are not presented to avoid obscuringtechniques of the invention.

[0021] First inlet 187 connected to first reservoir 183 and second inlet189 connected to second reservoir 185 are configured to release themetal precursor in a vapor phase in the path of the FIB over substrate100. In one embodiment, first inlet 187 and second inlet 189 should bepositioned (hl) about 100 microns from the surface of substrate 100 andadjacent FIB aperture 181. FIG. 1 also shows that the first reservoir183 and second reservoir 185 are connected to controller 190. Controller190 controls the addition of the metals from first reservoir 183 andsecond reservoir 185 to chamber 150 and may automatically adjust firstinlet 187 and second inlet 189. Absent automated process control, firstinlet 187 and second inlet 189 may be positioned manually.

[0022] Third and fourth inlets (193, 196) connected to first and secondprecursor gas sources (194, 195) are conduits configured to releasemetal precursors in a gaseous phase to chamber 150. First and secondprecursor gas sources (194, 195) each deliver one precursor gas thatincludes at least one or more metals. Controller 190 also controls theaddition of first and second precursor gases into chamber 150 and mayautomatically adjust third and fourth inlets (193, 196). Third andfourth inlets may also be manually adjusted.

[0023] There are numerous methods in which more than one metal may beintroduced into chamber 150 in order to form an alloy layer over asubstrate. One method is to premix the metals or organic precursorscontaining metals (e.g., tungsten hexacarbonyl, methylcyclopentadienyltrimethyl platinum, etc.) that may be in a powder form to a desiredratio by volume or by weight. For example, in terms of the volume offirst reservoir 183 and second reservoir 185, one liter of powder may beparsed into one-third for one metal and two-thirds for the other metal.The mixture of metals is then placed into one or both of first andsecond reservoirs (183, 185) for injection of the metals through firstinlet 187 or second inlet 189 into chamber 150. Alternatively,prealloyed precursors containing more than one metal may be prepared andplaced into first or second reservoir (183, 185). Prealloyed precursorsare created from conventional techniques such as mechanical alloying,jet mill processes, or other suitable methods. The combination of thesetwo metals is placed in the path of the FIB and after the FIB contactsthe metal precursors, the metals react and form an alloy layer oversubstrate 100.

[0024] In another embodiment, each metal (or metal precursors) may beseparately introduced at about the same time to chamber 150 to form analloy layer, during the reaction with the FIB, over substrate 100. Forexample, first inlet 187 to chamber 150 may introduce cobalt (e.g.,cobalt carbonyl) and second inlet 189 connected to chamber 150introduces molybdenum. The FIB strikes the metals (or metal precursors)causing the metals to react and form an alloy over substrate 100. Inthis embodiment, each metal may be subject to particular conditions forthat metal since each metal is separately introduced into chamber 150.

[0025] In yet another embodiment, metals (or metal precursors) may beinjected as a mixture or as a single metal (or metal precursor) in agaseous phase into chamber 150 below the FIB through first precursor gassource 194 and second precursor gas source 195 by way of third andfourth inlets (193, 196). If the metals are introduced into chamber 150in the gaseous phase, the gaseous phase then becomes a vapor based uponthe pressure in the chamber. It will be appreciated that each metalprecursor may have a different vapor pressure that may affect the amountof metal or metals that are introduced into chamber 150 illustrated inFIG. 1. As a result, the amount of each metal (or metal precursor)introduced into chamber 150 may depend upon the vapor pressure of thatparticular metal precursor. For example, the vapor pressure of di-cobaltoctacarbonyl precursor Co₂(CO)₈ is about three times that of tungstenhexacarbonyl precursor W(CO)₆. Accordingly, approximately two times ofthe amount of tungsten hexacarbonyl must be added to di-cobaltoctacarbonyl to achieve about 10% by weight of cobalt in the depositedmaterial alloy.

[0026] Once the metals (or metal precursors) in the vapor phase havebeen introduced into chamber 150, the FIB may be activated through FIBcolumn 175 or, alternatively, the FIB may be continuously activated. FIBcolumn 175 is coupled to chamber 150 and enters through a top surface ofthe otherwise sealed chamber. FIB column 175 includes physical deliverysystem 180 for introducing a species, including but not limited to agallium species, and energy source 182 (e.g., 50 kV HV power supply) forionizing the species and delivering the species to the substrate. Theamount of species introduced is also regulated by FIB aperture(s) 181 atthe base of FIB column 175.

[0027] In one embodiment, FIB column 175 is a Micron 9800FC columnproduced by FEI Corporation of Hillsboro, Oregon (www.feico.com). It isto be appreciated that other FIB columns may be similarly suitable.

[0028] For a 0.10 micron thick interconnect, an acceleration voltage orenergy source for FIB column 175 in the range of 30-50 kilovolts (kV) issuitable. In one example, the beam characteristics of 50 kV for a Micron9800FC are 569 picoamps (pA) with a pixel spacing of 0.025 microns by0.025 microns. A chamber pressure of about 1×10⁻⁷ Torr is established.

[0029] In another embodiment of introducing metals to chamber 150 toform an alloy layer, at least one metal is introduced through one of thetechniques described herein followed by another metal. In thisembodiment, a second metal line or a second metal layer is formed overthe first metal line or the first metal layer thereby forming amulti-metal layer over a substrate. This multi-metal layer is thenexposed to an alloy process. The alloy process includes either thermaltreatment (e.g., ambient heat, localized heating) of the multi-metallayer or exposure of the multi-metal layer to the FIB. These alloyprocesses cause the first metal line or first metal layer to react withthe second metal line or second metal layer to form an alloy layer overthe substrate.

[0030] Thermal treatment is created by heat source 191 and is applied toa multi-metal layer formed over substrate 100 in order to form an alloylayer. Heat source 191 may be either external or internal to FIBdeposition system 103. Heat source 191 may be a Light Amplificationthrough Stimulated Emission of Radiation (laser), oven, local ion scanbombardment, current forced through the metal line by an external powersource, or other suitable heat sources. The amount of heat that must beapplied to an alloy layer is dependent, in part, upon the metals ofwhich the alloy layer is composed. Generally, if a laser is used, about0.3 to 5 watts of heat is applied. The laser stage speed is typically inthe range of 0 to about 250μ/sec. The resistance of the alloy layer thatis created may be about 10 μΩ×cm to about 120 μΩ×cm.

[0031] In comparison, ovens generally heat an inert gas (e.g., argon) ata temperature up to 2000° C. in which a layer or layers are heated. Thesubstrate itself is protected from the heat by the combination of theaccuracy of the locally supplied heat and/or a heat exchanger (notshown). The heat exchanger, connected to substrate 100, is configured toremove heat from substrate 100.

[0032] Coupled to chamber 150 is controller 190. Controller 190 includesa processor (not shown) and memory 192. Memory 192 includes instructionlogic accessible by the processor to control the introduction ofmetal(s) and the FIB into chamber 150. Memory 192 also includesinstruction logic for applying heat to a multi-metal layer oversubstrate 100 to form an alloy layer. Alternatively, memory 192 includesinstruction logic to apply the FIB to the multi-metal layer to form analloy layer.

[0033] Controller 190 may control a variety of other parameters. Forexample, controller 190 may control the movement of heat source 191.Alternatively, substrate 100 of FIG. 1 itself may be moved to heatanother discrete area on a layer. It is to be appreciated, however, thatwith a suitable heat source, an entire interconnect area may be heatedat once.

[0034] Controller 190 also controls vacuum source 173 to ensure gasesgenerated in chamber 150 from heating a layer over substrate 100 areremoved. In this embodiment, gases such as carbon dioxide and carbonmonoxide that may be generated from heating the multi-metal layer areexhausted through exhaust 174. Other suitable instructions in controller190 are used to control other applicable control parameters.

[0035] Given the explanation of FIB deposition system 103, thedescription that follows in FIGS. 2 through 6 illustrates the formationof an integrated circuit structure in accordance with one embodiment ofthe invention. FIG. 2 illustrates a schematic cross-sectional view of aportion of typical semiconductor substrate or wafer 200 in accordancewith one embodiment of the invention. Substrate 200 generally comprisessilicon or other suitable material. Typically, substrate 200 includesdielectric layer 205. Dielectric layer 205 may include materials such assilicon dioxide, silicon nitride, or other suitable material.

[0036]FIG. 3 illustrates a schematic cross-sectional view of metalsintroduced onto substrate 200 illustrated in FIG. 2 using FIBdeposition. At least one or more metals such as the cobalt, metalcarbonyl, molybdenum, tungsten or other suitable metal is introduced tochamber 150. The metals may be introduced into chamber 150 by premixingmetal precursors in a powder form or using prealloyed precursors andplacing the metal precursors in a vapor phase. Alternatively, at leasttwo metal precursors may be introduced to chamber 150 in a gaseous phasethat is subsequently converted to a vapor phase.

[0037] A dose of the FIB may then be applied to the metals in the vaporphase. A dose is the rate of beam energy applied in nano-coulombs persquare micron (“nC/μm²”) of the FIB that contacts the metals in thevapor phase resulting in these metals forming an alloy layer such asfirst layer 210 over dielectric layer 205 at a rate of about 0.05μ/min.In still another embodiment, single metals or two or more metals may beintroduced into chamber 150 using techniques described herein resultingin the formation of a first metal layer over a substrate and a secondmetal layer over the first metal layer thereby creating a multi-metallayer. The multi-metal layer is then either hit by the FIB causing areaction between the first metal layer and the second metal layer toform an alloy layer or the multi-metal layer is thermally treated toform an alloy layer.

[0038] If the FIB deposition system is used, the depth of first layer210 is determined by the dose that is given to the metal molecules bythe FIB deposition system. Typically, first layer 210 of structure 212has a thickness of about 0.1 μm. First layer 210 is an alloy thatincludes, for example, two metals such as cobalt and molybdenum that areintroduced onto substrate 200 through FIB deposition. It will beappreciated that first layer 210 may also comprise another selection ofmetals.

[0039] Additional layers may be formed over first layer 210 as shown bysecond, third, and fourth layers (220, 230, 240) of structure 262 ofFIG. 4 using the techniques disclosed herein. Additional layers mayinclude more than one metal such as cobalt, metal carbonyl, molybdenum,tungsten, or other suitable metals. For example, second layer 220 mayinclude metals such as tungsten carbonyl and tungsten; third layer 230may include metals such as cobalt and molybdenum; and fourth layer 240may include metals such as tungsten and tungsten carbonyl. Moreover, thethickness of these layers may range from about 0.1 μm to about 0.3 μm.

[0040]FIGS. 5 and 6 are flow diagrams showing various methods forforming an alloy layer. FIG. 5 illustrates a flow diagram of one methodof FIB deposition of at least two metals to form an alloy layer over asubstrate in accordance with one embodiment of the invention. At block300, at least two metals are introduced to a FIB. In one embodiment, themetals are premixed in a powder form and then introduced into thechamber in a vapor phase. In another embodiment, prealloyed precursorsare introduced into the chamber in the vapor phase. In yet anotherembodiment, two or more precursor gases are introduced into the chamber.Each precursor gas contains at least one metal. The precursor gasesentering the chamber change to the vapor phase based upon the pressurein the chamber. At block 310, the FIB is introduced to a substratewithin a processing chamber. At block 320, a first alloy layer is formedover a substrate by the FIB. The resistance in the layer may range fromabout 120 μohm-cm to about 10 μohm-cm.

[0041]FIG. 6 illustrates a flow diagram of one method of forming analloy layer from a multi-metal layer over a substrate in accordance withone embodiment of the invention. At block 400, a first metal layer or afirst metal line is introduced to a substrate. At block 410, a secondmetal layer or a second metal line is formed over the first metal layeror first metal line creating a multi-metal layer. At block 420, analloying process is applied to the multi-metal layer causing the metalsto react and form an alloy layer. The alloying process includes thermaltreatment (e.g., ambient heating, local heating) or applying a FIB tothe multi-metal layer or multi-metal line. The resistance in the layermay range from about 120 μohm-cm to 10 μohm-cm.

[0042] In the preceding detailed description, the invention is describedwith reference to specific embodiments thereof. It will, however, beevident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the claims. The specification and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense.

What is claimed is:
 1. A method comprising: providing at least two metalconstituents; forming an alloy from the at least two metal constituentsby one of: (1) mixing the at least two metal constituents andintroducing the at least two metal constituents into a chamber in whicha focused ion beam contacts the at least two metal constituents to forma first alloy layer over a substrate; (2) introducing at about the sametime at least two precursor gas sources in which each precursor gassource contains a respective one of the at least two metal constituentsand the focused ion beam contacts the at least two precursor gases toform a first alloy layer over a substrate; and (3) forming a first layercomprising a first of the at least two metal constituents and a secondlayer comprising a second of the at least two metal constituents tocreate a multi-metal layer and performing one of thermal treatment andintroducing focused ion beam to at least a portion of the multi-metallayer to form a first alloy layer over a substrate.
 2. The method ofclaim 1, further comprising: forming more than one alloy layer over thesubstrate, wherein a second alloy layer is formed over the first alloylayer.
 3. The method of claim 1, wherein each of the at least two metalconstituents is selected from the group consisting of cobalt, metalcarbonyl, molybdenum, and tungsten.
 4. The method of claim 1, furthercomprising: forming more than one alloy layer, wherein a second alloylayer is formed over the first alloy layer.
 5. The method of claim 1,wherein the second alloy layer is created from a second multi-metallayer which is exposed to an alloy process.
 6. The method of claim 5,wherein an alloy process is one of thermal treatment and applying afocused ion beam to the first alloy layer.
 7. A system comprising: achamber configured to house a substrate for processing; an energy sourcecoupled to the chamber; a system controller configured to control theintroduction of at least two metal constituents to a focused ion beamand to control the introduction of the focused ion beam; and a memorycoupled to the controller comprising a computer-readable medium having acomputer-readable program embodied therein for directing operation ofthe system, the computer-readable program comprising: instructions forcontrolling the energy source and for introducing the metal constituentsby one of: (1) mixing the at least two metal constituents andintroducing the at least two metal constituents into a chamber in whicha focused ion beam contacts the at least two metal constituents to forma first alloy layer over a substrate; (2) introducing at about the sametime at least two precursor gas sources in which each precursor gassource contains a respective one of the at least two metal constituentsand the focused ion beam contacts the at least two precursor gases toform a first alloy layer over a substrate, and (3) forming a first layerof a first of the at least two metal constituents and a second layer ofa second of the at least two metal constituents to create a multi-metallayer and performing one of thermal treatment and introducing focusedion beam to at least a portion of the multi-metal layer to form a firstalloy layer over a substrate.
 8. The system of claim 7, wherein each ofthe at least two metal constituents is selected from the groupconsisting of cobalt, metal carbonyl, molybdenum and tungsten.
 9. Thesystem of claim 8, further comprising: forming more than one alloylayer, wherein a second alloy layer is formed over the first alloylayer.
 10. The system of claim 9, wherein the second alloy layer iscreated from a second multi-metal layer which is exposed to an alloyprocess.
 11. The system of claim 10, wherein the alloy process involvesthe second multi-metal layer exposed to one of a thermal treatment andto a focused ion beam.
 12. A machine readable storage medium containingexecutable program instructions which when executed cause a system toperform a method comprising: controlling introduction of at least twometal constituents into a chamber; controlling a formation of an alloyfrom the at least two metal constituents by controlling one of: (1)introducing the at least two metal constituents into a chamber in whicha focused ion beam contacts the two metal constituents to form a firstalloy layer over a substrate; (2) introducing at about the same time atleast two precursor gas sources in which each precursor gas sourcecontains a respective one of the at least two metal constituents and thefocused ion beam contacts the at least two precursor gases to form afirst alloy layer over the substrate, and (3) forming a first layer of afirst of the at least two metal constituents and a second layer of asecond of the at least two metal constituents a multi-metal layer andperforming one of thermal treatment and introducing focused ion beam toat least a portion of the multi-metal layer to form a first alloy layerover a substrate.
 13. The machine readable storage medium of claim 12,the method further comprises: forming more than one alloy layer, whereina second alloy layer is formed over the first alloy layer.
 14. Themachine readable storage medium of claim 12, wherein the method furthercomprises: controlling a formation of a second alloy layer over thesubstrate.
 15. The machine readable storage medium of claim 12, whereineach of the at least two metal constituents is selected from the groupconsisting of cobalt, metal carbonyl, molybdenum, and tungsten.
 16. Themethod of claim 14, wherein the method further comprises: an alloyprocess to the second alloy layer.
 17. The machine readable storagemedium of claim 16, wherein the alloy process is one of thermaltreatment and applying a focused ion beam to the second alloy layer.